Burner and boiler equipped with burner

ABSTRACT

A burner ( 10 ) includes a main combustion unit ( 20 ) configured to combust preliminary mixture gas obtained by mixing fuel gas and air at a first air ratio, and a plurality of flame stabilizing units ( 30 ) located to interpose the main combustion unit ( 20 ) and configured to combust preliminary mixture gas of a second air ratio that is lower than the first air ratio and achieves stable formation of flame.

BACKGROUND

1. Technical Field

The present invention relates to a burner and a boiler equipped with the burner. This application claims a priority right on the basis of JP 2013-162311 filed on Aug. 5, 2013 in Japan and its contents are incorporated herein by reference.

2. Description of the Related Art

There has been conventionally proposed a preliminarily mixing burner configured to preliminarily mix fuel gas and combustion air at a predetermined ratio and jet to combust the preliminary mixture gas thus preliminarily mixed, see Patent Literature JP 2006-220373 A and similar known art. Such a preliminarily mixing burner can preliminarily mix fuel gas and combustion air and then combust the mixture gas, so as to improve combustion efficiency of the fuel gas.

In recent years, a boiler or the like equipped with the burner has been strongly required to reduce toxic substances such as NO_(X) contained in exhaust gas generated by combusting fuel gas.

BRIEF SUMMARY Technical Problems

NO_(X) contained in exhaust gas can be reduced in concentration by decreasing as much as possible combustion temperature of the fuel gas at the burner. One way to decrease in combustion temperature of the fuel gas at the burner is increasing the ratio of the combustion air (air ratio) contained in the preliminary mixture gas. However, if the air ratio of the preliminary mixture gas is increased excessively, the burner cannot stably keep the flame lit and fails to stably combust the fuel gas.

In view of the above, one object of the present invention is to provide a burner configured to reduce a concentration of NO_(X) contained in the exhaust gas and combust stably, as well as a boiler equipped with such a burner.

Solutions to Problems

The present disclosure relates to a burner including: a main combustion unit configured to combust preliminary mixture gas obtained by mixing fuel gas and air at a first air ratio; and a plurality of flame stabilizing units located to interpose the main combustion unit and configured to combust preliminary mixture gas of a second air ratio that is lower than the first air ratio and achieves stable formation of flame.

Preferably, the burner further includes: a first supply line configured to supply the flame stabilizing units and the main combustion unit with the preliminary mixture gas of the second air ratio; and a second supply line configured to supply the main combustion unit with air.

Preferably, the main combustion unit includes a plurality of divisional main combustion units, and the flame stabilizing units are located to interpose each of the divisional main combustion units.

Preferably, the plurality of divisional main combustion units horizontally jets preliminary mixture gas and is disposed at a predetermined lateral interval, and the flame stabilizing units are disposed on both sides of each of the divisional main combustion units.

The present disclosure also relates to a boiler including: a boiler body; a plurality of water pipes disposed in the boiler body and extending vertically; a lower header disposed below the plurality of water pipes; an upper header disposed above the plurality of water pipes; an air supply duct having a tip end connected to the boiler body and configured to supply the boiler body with combustion air and fuel gas; and a burner disposed at a connection portion between the boiler body and the air supply duct; wherein the burner corresponds to any one of the burners described above.

Advantageous Effects of Invention

The present disclosure describes a burner configured to reduce a concentration of NO_(X) contained in exhaust gas and combust stably, as well as a boiler equipped with such a burner.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a longitudinal sectional view of a boiler equipped with a burner according to the present invention.

FIG. 2 is a sectional view taken along line A-A indicated in FIG. 1.

FIG. 3 is a view of an entire configuration of the burner.

FIG. 4 is a horizontal sectional view of the burner, schematically depicting a structure of the burner according to an embodiment of the present invention.

FIG. 5 is a graph indicating the relation among an exhaust gas O₂ concentration, an NO_(X) concentration, and a CO concentration according to each of an example and a comparative example.

DETAILED DESCRIPTION

A burner and a boiler according to a preferred embodiment of the present invention will now be described with reference to the drawings.

The burner according to the present embodiment is a preliminarily mixing burner configured to preliminarily mix fuel gas and combustion air at a predetermined ratio and jet to combust the preliminary mixture gas thus preliminarily mixed. This burner is applied to a small once-through boiler (hereinafter, simply referred to as a “boiler”).

As depicted in FIGS. 1 and 2, a boiler 1 according to the present embodiment includes a boiler body 11, a plurality of water pipes 12, a coupling wall 13, a lower header 14, an upper header 15, an air supply duct 16, an exhaust cylinder 17, and a burner 10.

The boiler body 11 is a rectangular parallelepiped body having a rectangular shape in a planar view.

The plurality of water pipes 12 extends vertically and is disposed inside the boiler body 11 at predetermined intervals in the longitudinal direction and the width direction of the boiler body 11.

The plurality of water pipes 12 according to the present embodiment is categorized into an outer water pipe group 12 a, a central water pipe group 12 b, and a midway water pipe group 12 c. The outer water pipe group 12 a is disposed along a lateral portion extending in the longitudinal direction of the boiler body 11 close to outer ends in the width direction. The central water pipe group 12 b is disposed in the longitudinal direction in the center in the width direction of the boiler body 11. The midway water pipe group 12 c is disposed between the outer water pipe group 12 a and the central water pipe group 12 b.

The coupling wall 13 couples the water pipes 12 disposed adjacent to each other in the outer water pipe group 12 a.

The lower header 14 is provided as a rectangular parallelepiped container having a rectangular shape in a planar view and is disposed at the bottom of the boiler body 11. The lower header 14 is connected with lower ends of the plurality of water pipes 12. The lower header 14 is supplied with water used for generation of steam from a water supply source (not depicted) and the lower header 14 supplies the plurality of water pipes 12 with water.

The upper header 15 is provided as a rectangular parallelepiped container having a rectangular shape in a planar view and is disposed at the top of the boiler body 11. The upper header 15 is connected with upper ends of the plurality of water pipes 12. Steam generated in the plurality of water pipes 12 is collected at the upper header 15. The steam collected at the upper header 15 is supplied to a loading machine (not depicted) that uses steam.

The air supply duct 16 is connected to a lower end of a first side surface 11 a located at a first end in the longitudinal direction of the boiler body 11. The air supply duct 16 is connected, at an upper stream end, with a tip end of a fuel supply line 161 supplied with fuel gas and a blower 18 configured to supply combustion air. The air supply duct 16 allows preliminary mixture gas, which is obtained by mixing fuel gas supplied from the fuel supply line 161 and combustion air supplied from the blower 18, to flow therethrough, and supplies the preliminary mixture gas into the boiler body 11.

The burner 10 is disposed in the first side surface 11 a at a connection portion between the air supply duct 16 and the boiler body 11. The burner 10 jets preliminary mixture gas obtained by mixing combustion air and fuel from the air supply duct 16 into the boiler body 11 so as to combust the preliminary mixture gas. The burner 10 is to be described in detail later.

The exhaust cylinder 17 is connected to a second side surface 11 b located at a second end (an end opposite to the end provided with the air supply duct 16) in the longitudinal direction of the boiler body 11. The exhaust cylinder 17 discharges, as exhaust gas, combustion gas generated by combustion of the preliminary mixture gas in the boiler body 11.

The burner 10 according to the present embodiment will be described in detail next with reference to FIGS. 3 and 4.

As depicted in FIGS. 3 and 4, the burner 10 according to the present embodiment includes a main combustion unit 20, a plurality of flame stabilizing units 30, a first supply line L1, and a second supply line L2.

The main combustion unit 20 combusts preliminary mixture gas having a first air ratio. The first air ratio is set to a value approximate to an air ratio achieving a theoretical combustion lower limit. The first air ratio is accordingly set to the so-called ultrahigh air ratio. Specifically, the first air ratio is preferably from 7% to 11% and more preferably from 8% to 10% when converted to a concentration of exhaust gas O₂ in order to effectively reduce a concentration of NO_(X) in the exhaust gas.

The air ratio is expressed by the value of an actually combusted air volume/a theoretically combusted air volume, and this value corresponds to the concentration of exhaust gas O₂ (%) in a predetermined relation. Accordingly, the air ratio is indicated by the concentration of exhaust gas O₂ (%) in this description. An NO_(X) value indicates a value converted at 3% as the concentration of exhaust gas O₂. A CO value indicates not a converted value but a read value.

The main combustion unit 20 according to the present embodiment includes a plurality of divisional main combustion units 21. More specifically, the plurality of divisional main combustion units 21 is disposed at predetermined lateral (horizontal) intervals. The divisional main combustion units 21 each jet preliminary mixture gas horizontally toward the interior of the boiler body 11. The divisional main combustion units 21 according to the present embodiment are aligned in two rows.

The plurality of flame stabilizing units 30 combusts preliminary mixture gas having a second air ratio. The second air ratio is set to a value lower than that of the first air ratio and allowing flame to be formed stably. Specifically, the second air ratio is preferably from 6% to 10% and more preferably from 7% to 9% when converted to a concentration of exhaust gas O₂ in order to stably keep flame at the burner 10.

The plurality of flame stabilizing units 30 is located to interpose the main combustion unit 20. The plurality of flame stabilizing units 30 jets preliminary mixture gas horizontally toward the interior of the boiler body 11. The flame stabilizing units 30 according to the present embodiment are aligned on the both sides of each of the two divisional main combustion units 21.

The first supply line L1 supplies the flame stabilizing units 30 and the main combustion unit 20 with preliminary mixture gas of the second air ratio. Preliminary mixture gas flowing through the air supply duct 16 is set to have the second air ratio in the present embodiment. The first supply line L1 is thus configured by the air supply duct 16 (see FIG. 1).

The second supply line L2 supplies the main combustion unit 20 with air. The second supply line L2 according to the present embodiment is configured by a pipe inserted through the air supply duct 16. The second supply line L2 has branching tip ends disposed in the vicinity of the plurality of divisional main combustion units 21, respectively (see FIG. 4).

Fuel gas supplied to the main combustion unit 20 is preferably from 50% to 95% and more preferably from 70% to 90% in volume of fuel gas supplied to the burner 10 in order to reduce the concentration of NO_(X) contained in exhaust gas and stably keep flame.

Operation of the boiler 1 according to the present embodiment will be described next.

Initially, combustion air supplied from the blower 18 and fuel gas supplied from the fuel supply line 161 are preliminarily mixed in the air supply duct 16. The fuel gas and the combustion air are preliminarily mixed to have the second air ratio in the air supply duct 16. The preliminary mixture gas thus preliminarily mixed to have the second air ratio is supplied to the main combustion unit 20 (the plurality of divisional main combustion units 21) and the plurality of flame stabilizing units 30.

The second supply line L2 supplies the plurality of divisional main combustion units 21 with air. Accordingly, the preliminary mixture gas jetted from the plurality of divisional main combustion units 21 is higher in air ratio than the preliminary mixture gas jetted from the flame stabilizing units 30. Specifically, the second supply line L2 supplies air of a volume set such that the preliminary mixture gas jetted from the divisional main combustion units 21 has the first air ratio.

The plurality of divisional main combustion units 21 jets the preliminary mixture gas of the first air ratio into the boiler body 11 so as to be combusted therein.

The plurality of flame stabilizing units 30 jets the preliminary mixture gas of the second air ratio into the boiler body 11 so as to be combusted therein. The plurality of flame stabilizing units 30 according to the present embodiment is located to interpose the plurality of divisional main combustion units 21. In this arrangement, the divisional main combustion units 21 configured to combust preliminary mixture gas of a high air ratio (the first air ratio) are interposed between the flame stabilizing units 30 configured to more stably combust preliminary mixture gas of a low air ratio (the second air ratio). Flame can thus be maintained even in a case where the divisional main combustion units 21 each combust preliminary mixture gas of a higher air ratio. The main combustion unit 20 includes the plurality of divisional main combustion units 21, and the plurality of flame stabilizing units 30 is disposed on the both sides of each of the divisional main combustion units 21. In this arrangement, the main combustion unit 20 (each of the divisional main combustion units 21) can have smaller flame (in width). The main combustion unit 20 is unlikely to cause imperfect combustion so as to reduce the concentration of CO contained in the exhaust gas.

The plurality of water pipes 12 is heated by combustion gas generated by combustion of the preliminary mixture gas jetted from the burner 10, and steam is generated from water supplied into the plurality of water pipes 12. The steam generated in the plurality of water pipes 12 is collected at the upper header 15 and is then supplied to the loading machine.

The combustion gas used for generation of steam in the boiler body 11 is discharged from the exhaust cylinder 17 as exhaust gas. The burner 10 according to the present embodiment combusts preliminary mixture gas of a higher air ratio and thus suppresses excessive increase in combustion temperature of the preliminary mixture gas. The concentration of NO_(X) contained in the exhaust gas can thus be reduced.

The burner 10 and the boiler 1 equipped with the burner 10 according to the present embodiment described above exert the following effects.

(1) The burner 10 includes the main combustion unit 20 configured to combust preliminary mixture gas of the first air ratio and the plurality of flame stabilizing units 30 located to interpose the main combustion unit 20 and configured to combust preliminary mixture gas of the second air ratio lower than the first air ratio. The main combustion unit 20 can combust in the state of being interposed between the flame stabilizing units 30 configured to stably form flame. The flame can thus be kept even when the main combustion unit 20 combusts preliminary mixture gas of a higher air ratio. The flame can be kept even when preliminary mixture gas of a higher air ratio is combusted, so as to achieve decrease in concentration of NO_(X) contained in exhaust gas as well as stable combustion at the burner 10.

(2) The burner 10 includes the first supply line L1 configured to supply the main combustion unit 20 and the flame stabilizing units 30 with preliminary mixture gas of the second air ratio and the second supply line L2 configured to supply the main combustion unit 20 with air. The burner 10 including the main combustion unit 20 and the flame stabilizing units 30 can thus be configured simply.

(3) The main combustion unit 20 includes the plurality of divisional main combustion units 21, and the flame stabilizing units 30 are located to interpose the divisional main combustion units 21, respectively. In this arrangement, each of the divisional main combustion units 21 can have smaller flame (in width). The main combustion unit 20 is thus unlikely to cause imperfect combustion so as to reduce the concentration of CO contained in exhaust gas.

(4) In the burner 10 configured to horizontally jet preliminary mixture gas, the plurality of divisional main combustion units 21 is disposed at lateral intervals and the flame stabilizing units 30 are disposed on the both sides of each of the divisional main combustion units 21. The burner 10 configured to form flame extending horizontally can thus suppress generation of NO_(X) in exhaust gas and achieve stable combustion.

Example

Advantageous effects of the present invention will now be described in more detail below with reference to an example and a comparative example. However, the scope of the present invention is not limited to the example.

Using the burner 10 (see FIG. 4) according to the example, in which the main combustion unit 20 includes the two divisional main combustion units 21 and the flame stabilizing units 30 are disposed at the top and the bottom of these two divisional main combustion units 21, respectively, variation in concentration of NO_(X) and variation in concentration of CO contained in exhaust gas were measured in a case where preliminary mixture gas has a varied air ratio (exhaust gas O₂ concentration).

In the present example, the boiler has the capacity of 3 t/h, the burner 10 was supplied with fuel gas (13A) of 170 m³N/h during high combustion (100% combustion), the main combustion unit 20 was supplied with 80% of the fuel gas, and the flame stabilizing units 30 were supplied with 20% of the fuel gas. The air ratio was regulated by varying the volume of combustion air supplied to the first supply line L1. Furthermore, the second supply line L2 supplied air of 220 m³N/h.

In the comparative example, the burner 10 according to the example was used and the second supply line L2 did not supply air.

FIG. 5 indicates results thereof.

As indicated in FIG. 5, the burner 10 could not combust when the exhaust gas O₂ concentration reached about 9.0% in the comparative example whereas the burner 10 could keep combustion (flame) until the exhaust gas O₂ concentration reached about 9.8% in the example.

When the exhaust gas O₂ concentration is in the wide range from about 7.6% to about 9.8%, the burner 10 is caused to combust with the concentration of NO_(X) contained in exhaust gas being suppressed to a quite low state of not more than 6 ppm.

Furthermore, the CO concentration rises when the exhaust gas O₂ concentration exceeds about 9.3%.

According to the results described above, it is found that the burner 10 can stably combust at the exhaust gas O₂ concentration of about 9%, at which level it had been difficult to stably combust preliminary mixture gas.

The burner 10 and the boiler 1 according to the preferred embodiment of the present invention have been described so far. The present invention should not be limited to this embodiment but can be modified where appropriate.

For example, the main combustion unit 20 according to the present embodiment includes the two divisional main combustion units 21. The present invention is, however, not limited to this case. The main combustion unit can alternatively include three or more divisional main combustion units. The main combustion unit can still alternatively include only one divisional main combustion unit.

The divisional main combustion units 21 according to the present embodiment are disposed at the predetermined lateral intervals. The present invention is, however, not limited to this case. Alternatively, the divisional main combustion units can be disposed at predetermined intervals in the height direction. Still alternatively, the divisional main combustion units can be disposed at predetermined intervals in the longitudinal and lateral directions (in the height direction and in the horizontal direction) and the flame stabilizing units can be located to interpose each of the divisional main combustion units.

The burner 10 configured to horizontally jet preliminary mixture gas is applied in the present embodiment of the present invention. The present invention is, however, not limited to this case. The present invention can adopt a burner configured to vertically jet preliminary mixture gas.

The burner 10 according to the present invention is applied to the small once-through boiler 1 in the present embodiment. The present invention is, however, not limited to this case. Alternatively, the burner according to the present invention is applicable to a different heating device such as a water heater or a reheat combustor of an absorption refrigerator.

The present invention can be embodied in other various modes without departing from the spirit or the leading features thereof. The embodiment or the example described above are thus merely exemplary on any points and should not be interpreted limitedly. The scope of the present invention is to be recited in the claims and is never restricted by the description. Any modification and alteration within the equivalent range of the claims are made within the scope of the present invention.

REFERENCE NUMBER LIST

-   -   1 Once-through boiler     -   10 Burner     -   11 Boiler body     -   12 Water pipe     -   14 Lower header     -   15 Upper header     -   16 Air supply duct     -   20 Main combustion unit     -   21 Divisional main combustion unit     -   30 Flame stabilizing unit     -   L1 First supply line     -   L2 Second supply line

The various embodiments described above can be combined to provide further embodiments. All of the U.S. patents, U.S. patent application publications, U.S. patent applications, foreign patents, foreign patent applications and non-patent publications referred to in this specification and/or listed in the Application Data Sheet are incorporated herein by reference, in their entirety. Aspects of the embodiments can be modified, if necessary to employ concepts of the various patents, applications and publications to provide yet further embodiments.

These and other changes can be made to the embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the disclosure. 

1. A burner comprising: a main combustion unit configured to combust preliminary mixture gas obtained by mixing fuel gas and air at a first air ratio; and a plurality of flame stabilizing units located to interpose the main combustion unit and configured to combust preliminary mixture gas of a second air ratio that is lower than the first air ratio and achieves stable formation of flame. 2-5. (canceled)
 6. The burner according to claim 1, further comprising: a first supply line configured to supply the flame stabilizing units and the main combustion unit with the preliminary mixture gas of the second air ratio; and a second supply line configured to supply the main combustion unit with air, wherein the main combustion unit and the flame stabilizing units are provided as areas where the preliminary mixture gas is combusted, and are disposed on a downstream side of the first supply line and the second supply line.
 7. The burner according to claim 6, wherein: the first air ratio is from 7% to 11% when converted to a concentration of exhaust gas O₂, and the second air ratio is from 6% to 10% when converted to the concentration of exhaust gas O₂.
 8. The burner according to claim 7, wherein: the main combustion unit includes a plurality of divisional main combustion units, and the flame stabilizing units are located to interpose each of the divisional main combustion units.
 9. The burner according to claim 6, wherein: fuel gas supplied to the main combustion unit is from 50% to 95% in volume of fuel gas supplied to the burner, and fuel gas supplied to the flame stabilizing units is from 5% to 50% in volume of the fuel gas supplied to the burner.
 10. The burner according to claim 8, wherein fuel gas supplied to the main combustion unit is from 50% to 95% in volume of fuel gas supplied to the burner, and fuel gas supplied to the flame stabilizing units is from 5% to 50% in volume of the fuel gas supplied to the burner.
 11. A boiler comprising: a boiler body; a plurality of water pipes disposed in the boiler body and extending vertically; a lower header disposed below the plurality of water pipes; an upper header disposed above the plurality of water pipes; and a burner having a main combustion unit configured to combust preliminary mixture gas obtained by mixing fuel gas and air at a first air ratio that is from 7% to 11% when converted to a concentration of exhaust gas O₂, and a plurality of flame stabilizing units configured to combust preliminary mixture gas of a second air ratio that is from 6% to 10% when converted to the concentration of exhaust gas O₂ and achieves stable formation of flame.
 12. The boiler according to claim 11, comprising: a first supply line configured to supply the flame stabilizing units and the main combustion unit with the preliminary mixture gas; and a second supply line configured to supply the main combustion unit with air.
 13. The boiler according to claim 12, wherein fuel gas supplied to the main combustion unit is from 50% to 95% in volume of fuel gas supplied to the burner, and fuel gas supplied to the flame stabilizing units is from 5% to 50% in volume of the fuel gas supplied to the burner. 